Referring to FIG. 1 and FIG. 2, FIG. 1 is a front view of a conventional expansion screw, and FIG. 2 is a partial sectional view of the expansion screw shown in FIG. 1. The expansion screw shown in FIG. 1 and FIG. 2 comprises a screw shank 10, a nut member 20, and a taper head 30. The screw shank 10 having a first end and a second end includes: an expansion hole 14 shown in FIG. 2, which extends a distance along the axis of the screw shank 10 from the first end toward the second end; a slot 16 located on the expansion hole 14, for communicating the expansion hole 14 with the outer periphery of the screw shank 10; a holding portion 18, formed by a plurality of strip grooves 182 provided at the outer periphery of the screw shank 10 with respect to the expansion hole 14; and a screw threaded portion provided between the second end of the screw shank 10 and the holding portion 18, and having continuous threads around the outer periphery thereof. A nut member 20 is screwed onto the screw threaded portion. Additionally, the taper head 30 has a coarse end 302 and a small end 304, the small end 304 is inserted into the expansion hole 14. The holding portion 18 will expand outwards while the taper head 30 is pushed into the expansion hole 14.
In order to anchor the conventional expansion screw described hereinbefore in a concrete construction, rock, or stone, a hole which is fitted for the expansion screw has to be drilled first, and then it is inserted into the drilled hole, by the way of hitting or hammering. The taper head 30 is forced to urge against the expansion hole 14 and make the holding portion 18 be expanded. The conventional expansion screw thus can be anchored in the desired location. However, it is not always easy for a user to drill a hole with an optimum size for the expansion screw. Furthermore, a user has to drill a hole first, then insert the expansion screw and hit the end of the screw shank to anchor the expansion screw.